Multiple sclerosis (MS) is an autoimmune disease that develops when the immune system loses tolerance for myelin in the sheath wrapping axons of the central nervous system (CNS). Damage to the myelin sheath can result in paralysis, vision impairment, and other neurological complications that significantly diminishes MS patient quality of life. There is no cure and many MS therapies also eliminate beneficial immunity. One experimental strategy to specifically counter autoimmunity is the generation of regulatory cell types, such as regulatory T cells (TREGS). The goal of such approaches is to selectively suppress the inflammatory T and B cells that are overactive and target myelin through cytotoxic pathways or antibody generation, respectively. Generation of antigen-specific TREGS and tolerance that counter autoimmunity could provide long-lasting treatments, while preserving protective immunity. A new idea to promote TREGS is suppression of toll-like receptor (TLR) signaling. TLRs regulate a power set of pathways that regulate immunity and evolved to detect the pathogens associated molecular patterns to initiate inflammation and eliminate dangerous pathogens. While TLRs are well known for their role in pathogen detection, surprising new studies show TLRs are also over-active during autoimmunity. To harness TLR signaling, the Jewell lab developed a nanotechnology platform where a regulatory TLR ligand (GpG) is synthesized with myelin self-antigen (MOG) to ensure immune cells receive both the signals to promote myelin-specific TREGS. Since these nanomaterials ? termed immune polyelectrolyte multilayers (iPEMs) ? are built entirely from the immune signals, they display the cues at a high density to potently modulate immune function. Administration of the iPEMs containing GpG and MOG prevents disease-associated paralysis in the experimental autoimmune encephalomyelitis (EAE) mouse model of MS. While promising, these effects were transient, and required multiple, high doses of iPEM injections. To overcome these challenges, I will develop microneedle arrays (MNAs) to deliver iPEMs built from myelin self- antigen and regulatory TLR ligands directly to the skin. MNAs are small patches (~1 cm dia.) with polymer needles several hundred microns in length, designed to target the immune-rich layers in skin. Skin is our largest immunological organ and contains a high density of immune cells, with specialized phenotypes that are constantly surveying the skin for foreign pathogens. Recent evidence indicates that some of these immune cells have a unique ability to promote TREGS in vivo, which were then able to suppress symptoms of paralysis in a common mouse model of MS. These exciting and recent results suggest that if the tolerance biased immune cells in skin could be harnessed through their TLR signaling pathways, they may be directed towards a tolerogenic phenotype. The central hypothesis of this VA CDA-2 proposal is that tolerogenic iPEMs delivered through MNAs will drive tolerogenic phenotypes in skin-resident antigen-presenting cells that will migrate to draining lymph nodes (LNs) and instruct T cells toward a TREG phenotype that restrains autoimmunity in a mouse model of MS. To test this hypothesis, I have designed three specific aims to: 1) assemble iPEM coatings on MNAs and predict their efficacy in vitro, 2) deliver iPEMs to skin using MNAs to test efficacy and specificity in mouse models of MS, and 3) test the role of TREGS in promoting efficacy of iPEM coated MNAs and investigate tolerance biomarkers in skin- draining LNs. This approach will provide two unique opportunities to address both disease and quality of life issues facing Veterans and their families. First, leveraging the unique immune environment in skin to achieve antigen-specific tolerance for MS could improve therapeutic efficacy and specificity. Second, MNAs can be applied independently by MS patients with motor deficits, which would improve independence and compliance. Collectively, achieving these goals would elevate Veteran MS patient quality of life.